quote:If we were to turn east onto Highway 26 at Washtucna, we would soon be driving alongside the Palouse River. The Palouse River flows out of Idaho, passes through the towns of Palouse and Colfax, and meanders through the Palouse Hills. It forms a part of the border between Whitman and Adams Counties. Then, about 3½ miles east of Washtucna, at the very eastern border of Franklin County, this lazy, meandering river makes a sharp turn southward and flows in a straight line over rapids and falls for four miles. Then ......

I find no evidence of mulitple uplifts of the CRBs. The stair-stepped topography in this picture looks more like successive lava flows; with interflow deposits being the ledge-formers and flows being the cliff-formers.

So lava flows erode quickly, while "interflow deposits", by which I assume you mean sedimentary deposits, erode more slowly? And the layers in the canyon walls in the picture are predominately lava flows? Like 95% of the height of the canyon walls is lava flow layers? Seems like an awful lot, and what features from the picture are telling you this, besides the cliffs and ledges?

Stair-stepping topography is usually attributed to differential erosion. The Grand Canyon is a perfect example. It's the softer inter-flow deposits that erode easier and the lavas are resistant. But in the Columbia plateau it could be all lava with different degrees of resistance to erosion. An exception is both marine terraces and river terraces. Marine terraces form when uplift raises a wave-cut platform above sea level. River terraces form when uplift causes a stream to cut down into its own deposits while meandering across a flood plain. Repeated episodes of uplift can result in multiple levels of nested terraces, both river and marine. But those in the picture clearly are not terraces; the river is not cutting into its own deposits. Actually a small terrace can be seen in the bottom of the canyon next to the stream.

When I see a sudden change in the earth's features, I like to ask why. Why did a lazy, meandering river suddenly become a rushing rapids flowing as straight as a stick for four miles? And what made that river suddenly fall 185 feet, then again meander calmly down to the Snake River? ( Doesn't sound like uplift to me, taking billions of year to create such a fascinating site )

Asking why is good. The sudden change was due to the well documented Missoula Floods. Check out the Palouse Falls wiki.

Repzion writes:

Erratics. You've all haerd of Basin City right? Well it is built on gravel beds. Some local farmers sometimes find huge boulders in their fields - not just the basalt rock that we would expect in this area, but granite and metamorphic rock as well. These unusual rocks must have come from far away in the mountains. Geologists can trace them to their source in the Okanogan Highlands or even the Rocky Mountains. Since these rocks are out of place here in the Pasco Basin, they are called erratics. How did such large boulders move here from so far away? It doesn't sound like uplift to me.

You are correct that is not uplift.

But who was suggesting that glacial deposits were the result of uplift. Uplift explains sea shell on mountain tops not glacial erratics.

I live on a big pile of glacial erratics and gravels mostly the result of the Missoula floods. I can dig a hole in my backyard and find well rounded rocks that I recognize from regions to the north and north-east well up into Canada. This is not uplift but glaciers and the resulting flooding that occur over *tens of thousands* of years - that is why these hard stones of granite, siltstones, quartzite, basalt are so well rounded - a single cataclysmic flood does not explain this.

I know everyone is pouncing all over you using pictures and facts and stuff, this is largely because you are sourcing your material from tired sources which have already been countlessly refuted.

I want to back everything up a step and ask a few simple questions-

1) Do you honestly believe that there was a massive worldwide flood in which waters covered the world in it's entirety? That there was one man, his family and a boat full of animals which survived it? And that prior to this man and dinosaurs walked the earth together?

2) Why? Given what you see around you, why do you feel that a Flood best describes what you see? (And I don't mean because the Bible says so - I mean, "I witness flooding in my neighborhood and it killed all my local dinosaurs")

Looking at the three tiered vertical cliff faces on the left of the picture, what is it about the green portions in between that indicates they are not terraces. The roughly 45 degree angle of these terraces would be caused by till from the rock face above covered with a thin layer of gradually accumulated soil on which some low growing greenery has found purchase.

I understand that differential erosion rates cause different angles of slope retreat, but vertical slopes indicate rapid erosion, possibly even a series of waterfalls moving gradually upstream by a few inches per year.

Is the type of layer, basalt versus sedimentary, apparent to you from the photo? If so, what features in the photograph are you looking at to identify them? Or, given that "the Columbia plateau it could be all lava with different degrees of resistance to erosion", how do you tell that's the case versus differential uplift rates from the photo?

Or is the conclusion based on knowledge that uplift rates, once begun, tend to stay roughly constant or only change very slowly?

I looked up terraces, I was inferring an incorrect definition from your post. You gave me the right hint when you said "the river is not cutting into its own deposits," but I didn't follow it. Anyway, I'm not arguing that the green regions are built upon terraces. The cliff faces are obviously all rock, not river deposits.

So if there was a constant rate of uplift and a constant rate of river cutting down through basalt layers, then what must have happened to cause the tiered appearance. Let's just consider the top most stretch of vertical cliff face on the left and the greenery covered layers just below it. The rate of slope retreat is tiny compared to the rate of downcutting, so this cliff face is vertical or nearly vertical. The we reach some softer layers, now hidden behind the green covering, and given that they're softer the river cuts through them much more quickly. This should still yield a vertical cliff face, so I'm guessing that's what's hiding behind the green covering. But beneath the green covering is what? I'm guessing talus on a flat ledge. (Did I call it till before?)

So if there's a flat ledge covered with talus underneath the greenery, what caused the ledge? Seems to me only a pause in uplift, during which the exposed cliffs of the downcut continue retreating, could do this.

Looking at the three tiered vertical cliff faces on the left of the picture, what is it about the green portions in between that indicates they are not terraces.

I would call them ledges. They have loose material on them that sits at the angle of repose (more or less). They represent more easily erodable material.

The roughly 45 degree angle of these terraces would be caused by till ...

Well, talus...

...from the rock face above covered with a thin layer of gradually accumulated soil on which some low growing greenery has found purchase.

Correct.

I understand that differential erosion rates cause different angles of slope retreat, but vertical slopes indicate rapid erosion, possibly even a series of waterfalls moving gradually upstream by a few inches per year.

Actually, the other way around. Quickly eroding shales form things like Badlands or the Tonto platform. Resistant rocks form cliffs like the Palisades.

Is the type of layer, basalt versus sedimentary, apparent to you from the photo?

You will notice that I carefully called them 'interflow deposits' in my original post. They may be sediments, they may be breccias, they may be simply porous flow-tops. The added feature they would have is that water would reach daylight along these porous horizons so that plants could live there.

If so, what features in the photograph are you looking at to identify them?

All of the above: gentler slopes, vegetation, and a lot of field experience...

Or, given that "the Columbia plateau it could be all lava with different degrees of resistance to erosion", how do you tell that's the case versus differential uplift rates from the photo?

I've been there. I have worked in volcanic rocks most of my career. These CR Basalts were highly fluid lavas that spread out quickly from linear vents, possibly at some great distance from these outcrops.

Or is the conclusion based on knowledge that uplift rates, once begun, tend to stay roughly constant or only change very slowly?

No, but I looked up a reference at the USGS website looking for uplift of the Columbia River plateau and it was pretty clear. The only real uplift here has been to the north in the Okanogan area that has resulted in a gentle regional dip to the south. These are really quite young rocks.

So if there was a constant rate of uplift and a constant rate of river cutting down through basalt layers, then what must have happened to cause the tiered appearance.

There is no evidence of major uplift here. In fact, a positive gravity anomaly over the CR Plateau suggests the opposite at present. These are very dense tholeiitic basalts erupted over a about 1.5 ma starting at 16 ma. Not a lot has gone on there since then.

Let's just consider the top most stretch of vertical cliff face on the left and the greenery covered layers just below it. The rate of slope retreat is tiny compared to the rate of downcutting, so this cliff face is vertical or nearly vertical. The we reach some softer layers, now hidden behind the green covering, and given that they're softer the river cuts through them much more quickly. This should still yield a vertical cliff face, so I'm guessing that's what's hiding behind the green covering. But beneath the green covering is what? I'm guessing talus on a flat ledge. (Did I call it till before?)

So if there's a flat ledge covered with talus underneath the greenery, what caused the ledge? Seems to me only a pause in uplift, during which the exposed cliffs of the downcut continue retreating, could do this.

What actually happens is the same thing as the Grand Canyon. Weaker layers erode, thereby undermining the stronger layers. The stronger layers, with their vertical joint systems simply collaps along those joints. So, when erosion happens it is quite fast. The problem is that it happens episodically and, in the long run, is slow. This is part of the confusion regarding the Grand Canyon as well. That is why the erosion looks catastrophic, but still takes a long time to form the overall landform.

These CR Basalts were highly fluid lavas that spread out quickly from linear vents, possibly at some great distance from these outcrops.

Highly fluid, in fact stunningly so. I am unable to conceive of these basaltic flows that must of have had the viscosity of water and filled entire drainages with basalt 1000's of feet thick. I live on northwest margin of the Columbia complex and the basalts in our region originated from vents 100's of miles to the east.

edge writes:

These are really quite young rocks.

Yep Miocene the bulk around 17 to 12 mya.

I am just guessing but the terracing in the picture may be the result of the river getting a grip on the material at the interface between two flows. There are dozens of layers in the region and between each there are often ash, aggregate and paleosols providing a foot hold for erosional elements.